Rehearsals on Operating systems RAM and traditional memory in a

computer

Source: Partly from Per S. Laursen

EASJ - Partly from Per's slides 2

Internal memory

• What is internal memory anyway?• Just some chips that hold a certain

amount of data• In a modern computers the internal

memory typically consist of 2-16 Gigabyte

• What kind of data is stored? E.g. music on a mp3 file, that the CPU has to compute to turn it into music.

EASJ - Partly from Per's slides 3

Internal vs. external

• RAM as a kind of Internal storage has one big advantage: transfer of data between the CPU and RAM is pretty fast (several Gigabytes per. Seconds)

• Fast yes, - but compared to what?• But there are some major drawbacks:

– RAM is pretty expensive (compared to what?)– When power is turned off, all data disappear from the

internal storage– We therefore also need an external storage

EASJ - Partly from Per's slides 4

The external memory/storage

• Where does the data in the internal memory comes from? The data comes from the external storage

• What is the external storage? Overall, the same as the internal storage, ie a passive storage of data, BUT– Is usually much cheaper than RAM– Retains data when power is turned off

• Most common form of external storage in a modern PC is a hard drive

EASJ - Partly from Per's slides 5

A hard item…

• Moderne harddiske rummer typisk 200-1000 Gigabyte

• A hard disk drive includes a number of magnetic plates, where bits are stored, by magnetising a certain region of the plate

• Modern hard drives typically houses 300-4000 Gigabyte

EASJ - Partly from Per's slides 6

Harddrive vs. RAMHarddrive RAM

Typical amount in a PC

200-1000 GB 4-16 GB

Price per Gigabyte 0,50-1 kr. 50-200 kr.

Transfer rate 0,1-0,3 GB/sec 4-8 GB/sec

Saves data without electricity

Yes No

Technology Mechanical Electronically

EASJ - Partly from Per's slides 7

Harddrive vs. RAM

• In other words:• RAM:

– Very fast and stable, but– Very expensive, and does not save

data without power/electricity.

• Harddrive:– Very cheap and has a big capacity, and

saves data without power/electricity, but

– Very slowly, and is based on technic

Hard drive vs Solid State drive

• New: SSD (Solid State Drive).• Faster than Hard drive.• But more expensive

than Hard drive.

EASJ - Partly from Per's slides 9

Harddrive vs. SSDHarddrive SSD

Typical amount in a PC

200-1000 GB 64-256 GB

Price per Gigabyte 0,50-1 kr. 7-12 kr.

Transfer rate 0,1-0,3 GB/sec 4,8 - 6 GB/sec(SATA 3/6)

Saves data without electricity

Yes Yes

Technology Mechanical Electronically

EASJ - Partly from Per's slides 10

Is a computer ”born” with an Operating system (OS)?

• BIOS handles very basic actions as a keystroke, and the drawing of letters on the screen

• When a computer starts, the BIOS is set to start

• The main task of the BIOS is starting the right operating system

• BIOS is a chip in your PC

EASJ - Partly from Per's slides 11

Administration of programs• Last time we discussed what it means, when the virtual memory

is larger than the RAM.• When we start a program, it will be copied from the external

memory/storage to the internal storage(RAM), and set in motion

Operating system

Program

Program

Program

The internal storage (RAM)

EASJ - Partly from Per's slides 12

Administration of programs

• The operating system must "find room" for the program in the internal storage - what if there is no more space?

Internal storage

Program

Program

Program Program

Program Program

Program Program Program

Program

What now?

EASJ - Partly from Per's slides 13

Administration of programs• The operating system can use some of the external storage

(hard drive), as an "emergency extension" to the internal storage

Internal storage

Program

Program

Program Program

Program Program

Program Program Program

Additional(temporarily)

internal storage

Program