- The BIOS Manufacturer and version number.
- The BIOS date.
- Setup program key.
- System logo.
- The “Energy Star” logo.
- BIOS serial number.
The BIOS continues to conduct tests, which include the memory count test and “system inventory” test. If the BIOS supports the “plug and play” standard, it will detect and configure the relevant devices and display a message on the screen for each one it finds. A long with this message is a system configuration display; exactly what is contained in this summary will depend on the BIOS and system.
The BIOS has now completed its testing process and now actively searches for a drive to execute the boot sequence and load the operating system. The drive to boot from will depend on the settings placed in the BIOS (these setting can be changed), it could try the floppy disk (A:) or hard disk (C:) or even from a CD ROM. If searching the (C:) drive it will look at the master boot record at cylinder 0. If does not find what it is looking for it will go to the next disk in line. However, if it finds the appropriate instruction the BIOS will start the loading of the operating system. At this point the BIOS is now relieved and the boot sector completes the system initialisation.
2) Before a hard-drive can be used it must be initialized.
- Explain why thus must be done?
All disks have to be formatted, also known as “Initialisation”. This process allows the system to distinguish between tracks and sectors, by pre-programming data on the disk. Allowing every block of data to be uniquely addressed by the read/write head of the hard-drive. Therefore this initialisation is essential so that data can be stored or retrieved, without initialisation the hard-drive would not function correctly.
- Discuss the implications of the FAT32 system (e.g. cluster sizes, relation to FAT16 files etc.)
All disks hold there data in sectors and clusters (A cluster is simply a group of sectors.), in which a file can fit on more than one sector or cluster. Therefore there is a need to maintain a record of which sectors are in use by each file. A system used to allocate and address sectors or clusters in use, is called a ‘File Allocation Table’ or ‘FAT’.
The FAT is a fixed size and each entry refers to one allocation unit on the disk. This allocation unit can be one cluster for a hard disk or one sector for a floppy disk. If a hard disk had a cluster size of 4, this means there are 4 sectors referred to in one go, instead of each sector individually. It has the advantage of being able to be used for larger storage disks. But, has the disadvantage of wasting disk storage. This can be explained by; if the words “Mary had a little lamb” were to be saved as a file on disk, it would use one allocation unit of storage and not just the 22 bytes of the file e.g. one allocation unit on a 1.44 Mb floppy disk is one sector (512b), the file would use 512 bytes of storage. However, a hard drive with one cluster = 64 sectors as one allocation unit, the 22 byte file would use 64 x 512 = 32,768 or 32 Kb of storage. This wasted space is known as “slack”.
The reason that cluster sizes are fixed is that the FAT is fixed in size and will only address a fixed number of items. The concept of clusters is relatively new, as the older 16-bit FATs did not recognise clusters, which give them the limitation of only been able to address 216 = 65,536 sectors. As each sector is 512 bytes this meant the hard drive could only store (512 x 65,536) 32 Mb of data. If we now look at the same FAT able to recognize clusters with 64 sectors per cluster, it can now store 64 times as much data. The older FATs did not show their limitations at first, however as hard disks continued to increase in size the limitations were obvious. The use of large cluster sizes, as with the newer FAT 16 had large amounts of slack. Drive size eventually became too large and FAT16 could not be used to format a whole drive in a single partition. This led to FAT 16 becoming unwieldy and confusing to the average PC user. As PC’s seemed to come with more than one hard disk, which in fact were just different partitions on one disk.
FAT32 was created by “Microsoft” to elevate the above problems. It received its name because it uses 32-bit numbers to represent clusters vice the 16-bits used by FAT16. It relieved the FAT16 limitations by allowing single partitions of very large size, to be created. It also saved on “slack” by utilizing smaller clusters to that of FAT16. The table below shows a comparison between FAT16 and FAT32.
- Calculate the maximum theoretical storage size of a drive with a FAT that is 32 bits wide and a sector size of 512b?
Calculate the number of sectors = 232
Sectors = 4,294,967,296 (sectors)
512 bytes per sector. Therefore theoretical volume = 4,294,967,266 x 512 = 2.19912
Ans 2.199 Terabytes / 2Tb of data.
3) Batch files and scripts are commonly used in current systems.- Explain the purpose of batch files?
Many tasks require repeated keyboard commands to reproduce the same results. Placing them in a text file can relieve these mundane tasks. This file is called a ‘batch file’. The following are common uses for batch files:
- To automate regularly used DOS sequences.
- Create customized user menus e.g. displays program options.
- Automatically load and run a program when the PC is first initialised, and given the name “AUTOEXEC.BAT”
In essence, batch file can be described as simple time savers. They also save time by removing typing errors as the file has to be written only once and if it works, the batch file will work a second time.
- Design a simple batch file to create a new subdirectory for backups, if it does not already exist, and copy into it all the files in the current directory with the suffix “.doc”. The directory name for the backups should be supplied through the command line as a parameter?
“COPY CON BU.BAT” should be entered at the MS DOS prompt. This allows the data typed in “CONsole” to be copied into file BU.BAT.
The following is then entered:
@ECHO OFF (Switches off screen display of comments)
ECHO;
REM ****This program is designed to save a designated file extension e.g. “.doc”****
REM ****to the BACKUP file of the C: Drive
ECHO ****Written by D.J.WADE 27/04/03****
ECHO;
ECHO;
ECHO ***File backup in progress. ***
PAUSE
ECHO ****Creating new directory****
CD C:\BACKUP
COPY C: *.%1 C:\BACKUP
ECHO ****All .doc files copied over****
PAUSE
ECHO ****The contents of the BACKUP directory****
DIR C:\BACKUPS/P
ECHO ****All file have now been copied ****
When complete press ‘CTRL’ “Z” then {ENTER} to copy file.
Run batch file and copy all “.doc” files enter the following:
“BU doc” then press {ENTER}
- What role do the Config.sys and Autoexec.bat files have in the start-up process?
The CONFIG.SYS is a text file, which allows the user to alter a system’s default setting. Each text line contains a description of an alteration to the standard system configuration e.g. load appropriate hardware drives, allocation of disk buffers
AUTOEXEC.BAT is also a text file; it is checked and looked for after the process has conducted the CONFIG.SYS stage in configuration. It is an optional file, but if located its instructions are executed chronologically. It also runs automatically each time the system is initialised. The file has many uses because of this fact, one such use is to refine the machines configuration.
Both these file also have an important roll in the allocation and set up of the system memory.
4) The BIOS is an integral part of all PC systems.
- Briefly describe the main functions of the BIOS, and how it relates to the operating system, application programs and to the CMOS?
With one or two exceptions, the PC is controlled by software. It is the hardware that performs the tasks, under the control of the software. This software is stored on a disk and when the system is initialised it must be loaded into system memory RAM, before it can be used. As discussed in question one, this posed a problem as the memory is cleared when power is removed from volatile system memory. The solution to this was the ‘Basic Input/Output System’ also known as the BIOS program. The system BIOS is the lowest-level of software, providing an essential link between the hardware and the operating system.
Acting similar to that of a catalyst, the BOIS provides access to the hardware to enable the creation of the higher-level operating systems (e.g. DOS, Windows 95+, etc) that run applications. The BIOS start executing also immediately the PC has power applied. The most important function of the BIOS is the role it plays in the “boot” of the system. As already stated the system memory is volatile and looses it data once power is turned off. Therefore when the power is turned on, it needs to find instructions to tell it what it needs to do to restore the RAM and get the PC up and running. These integral instructions are found in the BIOS programs, which is available use as they are stored in non-volatile memory (ROM). It is also responsible for allowing the user to control the computer’s hardware settings.
The user sets these functions by utilising a small built-in utility, often called “the BIOS”. These setting now have to be stored in a memory store called the “CMOS”, which stands for ‘Complimentary Metal Oxide Semiconductor’. This technology has the advantage of requiring very small amounts of power in comparison to RAM. It can be powered by a small battery, which can last the life of the machine. It is therefore ideal device to store the BIOS setting. In addition to the CMOS the new plug and play BIOS’s use additional non-volatile memory to hold extended system configuration data (ESCD) e.g. resource configurations of system devices when plug and play is used.
As technology progressed and PC’s evolved, the system BIOS’s have had to evolve also. The earlier BIOS’s were stored in ROM and could not be altered once the manufacturer had pre-programmed them. This has now become too inflexible; fortunately technology has created the “flash BIOS”. This allows upgrades to be performed without having to add any further electronics to the PC. A special type of BIOS ROM called Electrically Erasable Programmable Read Only Memory or EEPROM is used to re-write the BIOS settings. This procedure is called “Flashing” the BIOS, hence the name Flash BIOS. This is a great break thru, however extreme caution should be taken when conduction the flashing process, as it is a vital program to get the PC up and running at initialization. An incorrect procedure could render your computer un-serviceable and need a new BIOS.
- What does “ROM shadowing” mean?
A limitation with ROM’s used as the system BIOS and the video BIOS, is that the access time is slow when compared to that of RAM. Access time for ROM is between 120 to 200 ns however, in comparison to RAM that is normally 50 to 70 ns. System RAM is also accessed 32 bits at a time, whilst ROM’s normally only 16 bits at a time. The overall resultant of this is that BIOS code is slower to access than code in the system memory. Therefore if the BIOS code and video code were held in RAM, their operations would be greatly enhanced, increasing the access speed and ultimately the systems performance.
Facilities exist to “mirror/copy” the ROM code into RAM to give this improved performance. The process used is called “ROM shadowing”. This shadowing can enabled or disabled via the BIOS setup and allows a choice of enabling either the system BIOS code, video BOIS code or both. The chosen ROM code is copied into the unused areas in the system area i.e. between 640K to 1 Mb.
