COMPUTER SCI.HARDWARE

MEMORY

MEMORY

Internal devices which the computer has direct access to. Temporary data/key data that the computer needs to run.

STORAGE

Allows the user to store applications.Permanent memory,Bigger size than memory as it store permanent and larger files. External device that can be disconnected from the computer.

Primary memory-RAM AND ROM

RAM(random access memory) Primary memory in which data can be read from or written to.

ROM(read only memory) Primary memory in which data can only be read from.

RAM-DRAM & SRAM

DRAM; makes use of capacitors( to store data in 1’s and 0’s), and transistors(allow chip control circuitry to read the value in the capacitor or to change its value). Needs to be frequently refreshed else value in the capacitor will be leaked. Used in main memory.

SRAM; makes use of flip flops to store data. Used in memory cache

SRAM AND DRAM (advantages and disadvantages)

NOTE:In cases where data needs to be accessed at fast rate, SRAM is used instead of DRAM e.g in cache memory.

• SRAM does not need to be frequently refreshed

• Faster access than the DRAM

• DRAM consumes less energy than the SRAM-when SRAM is used to access data at a higher frequency it consumes more power.

• DRAM has a higher memory capacity

• DRAM is less expensive.

ROM-PROM, EEPROM,EPROM

PROM-programmable ROM. Can only be written to once. Made up of a matrix of fuses. It alters specific cells by burning fuses in the matrix using an electric current. That is why it can be written to once. mobile phones,RFID tags.

When programming, a PROM writer is needed.

EPROM

Erasable PROM. made up of capacitors and transistors(floating gates). Uses UV light for programming in a quartz window. It’s used for programming/developing applications e.g games.

Secondary storage-HDD(magnetic)SSD,OPTICAL

HDD(hard disk drives)-made up of platters that can store data. Made up of read-write heads that moves from the Centre of the disk to the edge of the disk scanning the disk/reading data.They rely on magnetic properties. Platter→tracks→sectors. Sectors on a given track store a certain no. of bytes.

SSD(solid state drive)

Used in memory stick/pen drives.Stores data by controlling the movement of electrons in the NAND chip, data is stored as 1’s and 0’s in transitors(floating gate) the other gate is called the control gate. Has no moving parts. Makes use of EEPROM.

LATENCY

Time taken to find a track in a disk. It depends on the time taken by the disk to rotate around its read write head. The read write head constantly seeks the right bulk of data.

BENEFITS OF USING SSD OVER HDD

• SSD has no moving parts = reduced latency. It is more reliable.

• SSD is lighter as it has no moving parts hence more suitable for laptops

• Less power consumption as it is faster in data accessing/retrieval.

• Because of less power consumption it runs cooler than HDD.