Computer Memory & Software
Why memory?
A computer must remember the program it is running, the data it is working on and the results it produces. Memory is the part that stores all of these. Like a student who keeps today's books on the desk (fast to reach) and the rest in a cupboard (more space, slower to reach), a computer uses different kinds of memory.
Units of memory
The smallest unit is a bit (0 or 1). 4 bits = 1 nibble, 8 bits = 1 byte. Bigger units go up in steps of 1024 (2¹⁰).
photo_mb = 4
phone_gb = 128
photos = phone_gb * 1024 // photo_mb
print('Photos that fit:', photos)
print('In bytes:', phone_gb * 1024 ** 3)Types of memory
Primary memory: RAM and ROM
RAM
- Random Access Memory
- Read + write
- Volatile – erased when power is off
- Holds running apps and open files
- More RAM → smoother multitasking
ROM
- Read Only Memory
- Mostly read only
- Non-volatile – keeps data without power
- Holds BIOS / firmware to start the computer
- Small size
Cache memory
Cache is a small, very fast memory between the CPU and RAM. It keeps copies of the data and instructions used most often, so the CPU does not have to wait for slower RAM. Think of keeping your pen and calculator on the desk instead of in the bag.
Secondary memory
| Device | Technology | Note |
|---|---|---|
| Hard Disk Drive (HDD) | Magnetic | Cheap, large, has moving parts |
| Solid State Drive (SSD) | Flash memory | Fast, silent, no moving parts |
| Pen drive, SD card | Flash memory | Portable |
| CD / DVD / Blu-ray | Optical | Read with a laser |
| Cloud storage | Remote servers | Google Drive, OneDrive; needs internet |
What is software?
Software is a set of instructions (programs) that make the hardware do useful work. Without software, a computer is just a box of metal and plastic.
📁 Software/ ├── System 📁 software/ │ ├── Operating system Windows, Linux, Android │ ├── Device drivers printer, Wi-Fi drivers │ └── Utilities antivirus, backup, disk cleanup ├── Programming 📁 tools/ │ ├── Translators compiler, interpreter, assembler │ └── IDEs / editors IDLE, VS Code, Jupyter └── Application 📁 software/ ├── General purpose MS Word, Excel, browser └── Customised school ERP, hospital billing
System software
The operating system (OS) is the most important system software. It manages the CPU (which program runs when), memory (who gets how much RAM), files and folders, devices and security, and gives a user interface (GUI, touch, voice). Popular OS: Windows, macOS, Linux (Ubuntu), Android, iOS.
Utility software keeps the computer healthy: antivirus, file compression (ZIP), disk cleanup, backup and restore. Device drivers let the OS talk to hardware.
Programming tools and translators
Computers understand only machine language (0s and 1s). Translators convert programs written by people into machine language.
| Translator | Converts | How |
|---|---|---|
| Assembler | Assembly language → machine code | Instruction by instruction |
| Compiler | High-level (C, C++) → machine code | Whole program at once |
| Interpreter | High-level (Python) → machine code | One line at a time |
An IDE (Integrated Development Environment) like IDLE or VS Code combines an editor, a translator and a debugger in one window.
Application software
By licence, software is proprietary (paid, closed source – MS Office), freeware (free, closed source – Zoom basic) or free and open source (free, code available – Linux, Python, LibreOffice).
Summary & practice
- bit → byte (8 bits) → KB → MB → GB → TB → PB, ×1024 each.
- Registers → cache → RAM/ROM → secondary: speed falls, size grows.
- Software: system (OS, drivers, utilities), programming tools, application.
- Compiler: whole program; interpreter: line by line.
1) A 64 GB pen drive holds how many 512 MB videos? 2) Classify: Tally, antivirus, Python interpreter, Android, a printer driver. 3) Which memory loses its data when the phone switches off?
Answers: 1) 64 × 1024 ÷ 512 = 128 videos. 2) Application, utility, translator, OS, driver. 3) RAM.
