Computer Studies Paper 2, WASSCE (SC), 2018

Question 2

 

(a)  What is a register?
(b)  List two types of register.
(c)  State three functions of registers.
(d)  Outline three differences between register and main memory.

 

Observation

The expected answers were:
(a)       A register is a small holding area on the processor chip that works much like random access memory. The register holds program counters, data, instructions, and addresses that the arithmetic logic unit is currently processing.      
OR

A processor register (CPU register) is one of small set of data holding places that are part of the computer processor.
OR

A register may hold an instruction, a storage address, or any kind of data (such as a bit sequence or individual characters)
OR
Register is a special high speed storage area within the CPU. All data must be represented in the register before it can be processed

  • Data Register
  • Memory data register
  • Index register
  • Stack pointer register (SPR)
  • Condition code register
  • Interrupt control register
  • Temporary register
  • Permanent register

 

 (b)       Types of registers
  • Memory Address Register
  • Memory Buffer Register
  • Input/output Register
  • Input/output Buffer Register
  • Program Counter
  • Instruction Register
  • Accumulator Register
  • Flag Register
  

 

 

 

 


(c)       Functions of registers

  • Holds the address of memory where CPU wants to read or write data.
  • Holds the contents of data/instruction read from or written in memory.
  • Used to specify the address of a particular I/O device.
  • Used for exchanging data between the I/O module and the processor.
  • Used to store the address of the next instruction to fetch for execution
  • It stores current instruction being executed or coded
  • It allows the bits of its content to be moved to left or right (shift register)
  • It holds the memory addresses of data and instruction during execution phase
  • It is used to store the result produced by the system
  • It acts as a hardware element which holds a number that can be added/subtracted to/from address potion of computer instruction
  • It is used to temporarily store data being transmitted to/ from peripheral devices 

 

(d)       Differences between Register and Main Memory

Register

Main Memory

Loads/holds the instructions that the CPU needs

Holds the instructions and data that the currently executing program in the CPU requires

Holds the small amounts of data around 32 bits to 64 bits

Memory of the computer ranges from gigabytes to terabytes

CPU operates on the register at a faster rate

CPU operates on the memory at a slower rate

Examples are accumulator, program counter, instruction register, etc

Examples is random access memory

Some registers are located internally to the CPU

Located externally to the CPU

There are usually few registers on a processor

There are lot more registers in RAM

Registers in the CPU hold the data the processor is currently working on

RAM holds program instruction and data that program requires

    

   The question tested candidates’ knowledge of registers and main memory.
It was reported that candidates failed to differentiate between registers and main memory. A good number of the candidates were confused between computer registers and attendance register.