HARDWARE

Micro-computers are structurally similar to large computers in that they have the same basic components – CPU main memory, secondary memory and input/output devices. The most popular secondary memory device are floppy disk drives and fixed disks. Floppy disks store between 140 K Bytes to 1 Mega Byte = 1024 K Bytes (MB) while hard disks store 10 MB to 40 MB.

 

The main memory is made from several chips. These may be ROM or RAM chips.  ROM (Read Only Memory) chips contain instructions permanently written in the memory. The contents of these chips cannot be altered. RAM (Random Access Memory) Chips provide the memory that can be read from, written into and cleared.

 

Most micro-computers have between 16 K bytes and IMB memory. The typical word-size of micro-computers when they were introduced in business in the late seventies was B-bits. Today, the most common word-size is 16-bits. It is virtually certain that in the next few years 32-bit micro-computers will be very common although today their numbers are somewhat limited due to cost and scarcity of software. Dot matrix and daisy-wheel printers are popular printing devices on micro-computers.

Magnetic Disk-2

Each recording surface is divided into a series of concentric circles called tracks and each track is further divided into sectors. The capacity of each sector whether it is on the inner most track or outer most track is a constant. One important characteristic of a disk drive is the access time which represents the time needed to access the desired record from a disk. Access time consists of two components, namely, seek time and rotational delay. Seek time represents the time required to seek the desired track on the desired recording surface. This involves a movement of the access arm, which supports the read/write head. Rotational delay represents the time required for the rotating disk to position the desired sector under the read/write head. Access times of 35 milli seconds are common. Disk packs are classified into three types, namely, removable disks, fixed disks and Winchester disks. 

A removable disk pack, as the name indicates, can be transported and replaced. A fixed disk pack on the other hand, cannot be removed or transported or replaced. However, it provides a quicker access time. A disk storage capacity of 600-1000 MB is very common. Winchester disks are a special type of hard disks and are supported mainly by micro-computers. A Winchester disk provides a storage capacity in the range of 10 MB – 80 MB.

Main Memory-2

Today we continue our talk on Main memory as part of Computer Hardware. Earlier computers used magnetic core memory. However all modern computers use semi-conductor memory. Semi-conductor memory is faster and cheaper than magnetic core memory. Semi-conductor memory is also available in small board. These characteristics have made semi-conductor memory more popular and attractive. The only drawback of semi-conductor is that it is volatile. That is it loses its content is the event of power failure. However, it is not a serious drawback and can be easily overcome by having back-up power units.

 

Semi-conductor memory is known as RAM (random access memory). This means that any parts of memory can be accessed for reading and writing. A magnetic core memory is also called random access memory. However the terminology RAM has been used in the literature with invention of semi-conductor memory. Another part of main memory is ROM, (Read Only Memory). ROM allows its contents to be read only and dose not allow users to store their programmes supplied by the manufactures frequently used by the users.

 

RAM capacity is a useful indicator to compare the main memory capacity of various computers. Earlier computers, provided a memory of 16 KB, but a memory capacity of 512 KB is very common in today’s micro-computers.