1. Intro to computing
September 7, 2017

2. What is a computer? A computer is… a device that accepts data or input
and processes it in some way
to automatically produce
a result

3. What is a computer?
A computer is a device that accepts data or input and processes it in some way to automatically produce a result.
Computing refers to the computer doing any kind of work.
In the most general sense, “computing” means “calculating.”

4. Layers of abstraction
Computer systems are built upon the principle of (layers of) abstraction.
Abstraction is the practice of suppressing the details “under the surface”—you don’t know how something is being done, only that it gets done.
Think about BCPS—does the superintendent know every intricate detail about what happens in the system?
“Ms. White, someone left the toilet seat up in the first-floor faculty bathroom at Towson High again.”
In a computer system, each layer is an abstraction of the level below it.
The “virtual machines” (hypothetical computers) at each level execute their own instructions, calling upon machines at lower levels to perform tasks as necessary.

5. Input and output
A computer starts by taking in some sort of data or information, called input.
Traditional forms of input: mouse clicks, button presses, taps on a touch screen…
Less traditional forms: RPM (automatic transmission), temperature (thermostat), imperfections (automated assembly lines)…
Computers use these inputs to generate a result, called output.
Simplest example: whatever is displayed on the screen.

6. Algorithms
Computers use an algorithm to process the input and generate the desired output.
An algorithm is a set of rules/steps to follow.
Long division is one example of an algorithm!
Programming is the process of providing a computer with an algorithm in order to perform a particular task.

7. Computational process
The process of translating inputs into outputs is known as the computational process; this will often involving performing a series of calculations in the form of an algorithm.
All tasks computers perform require some sort of computation.
Simple: Typing “2 + 2” into your calculator.
More complicated: Calculating the fastest route from here to Disneyland.

8. Hardware and software
Computers require a combination of hardware (the physical devices that make up the computer itself) and software (the programs that run on the computer).
Much of a computer’s hardware is attached to the motherboard or logic board.
Input/output devices such as a keyboard, mouse, and monitor are known as peripherals.

9. Motherboard

10. How does it work? Start by pushing the power button on your computer.
This sends a signal to the power supply to energize the computer.
A piece of software called BIOS (Basic Input/Output System) starts up.
BIOS tells the computer what to do now that it has power.
This is stored on what is known as the BIOS chip.
Legacy BIOS has largely been replaced by Unified Extensible Firmware Interface (UEFI).

11. BIOS BIOS starts by initializing the CPU and memory.
BIOS makes sure the computer has the hardware components needed to load the operating system.
Is the CPU installed?
Is the CPU performing properly?
Is there memory (i.e., RAM) installed?
BIOS then confirms that the computer’s graphics card is operational.

12. POST
Finally: BIOS performs a series of “Power On Self-Tests” (POSTs) to confirm the hardware is functioning correctly.
First POST makes sure that the computer’s RAM is fully readable and writeable.
Next POST checks for peripherals (e.g., keyboard, mouse, speakers, monitor, printer…).

13. BIOS
BIOS configuration was formerly stored on the CMOS (Complementary Metal-Oxide Semiconductor), which is perhaps best known for maintaining the current date and time.
The CMOS had its own lithium backup battery so this information was not lost if the computer lost power.
Configuration is now stored on flash memory (non-volatile storage medium).
A non-volatile storage medium retains data in the absence of a power supply.
BIOS configuration allows you to change the order of boot disks.
Think Windows “recovery CDs”…

14. BIOS vs. UEFI
UEFI includes mouse support and typically includes a graphical user interface (GUI).
UEFI also includes a pre-boot environment that can be used to browse the Internet or back up files.
This is often used to troubleshoot the computer’s operating system.
This pre-boot environment is itself NOT an operating system.

15. Peripherals
Today, most peripherals are connected via USB (Universal Serial Bus).
Current standard: USB 3.1.
If you have a PC with USB 3.0+ ports, the slots will be blue and may include “SS” (for “SuperSpeed”) next to the USB marking.
Keyboard and mouse used to connect using PS/2 ports (purple for keyboard, green for mouse).
Printers (among other peripherals) used to connect using the parallel port, and later the serial port.
The relevant standards were known as SCSI (Small Computer System Interface).

16. Displays
External displays generally connect through one of three ports:
VGA (Video Graphics Array)
DVI (Digital Visual Interface)
HDMI (High-Definition Multimedia Interface)
HDMI has become the de facto standard.
VGA and DVI require a separate cable to transfer audio; HDMI does not.
VGA is analog; DVI and HDMI are digital.
The most expensive HDMI cable is not the “best”!
Unlike with analog cables, there is no way to improve the quality of a digital data transfer, which uses 0s and 1.
Something is either 0 or 1; there is no in-between.

17. Operating system
Once the POST process has completed, the BIOS can begin loading the operating system (Windows, macOS, Fedora, etc.).
The operating system’s code is stored on the hard drive, which connects to the motherboard via the SATA (Serial Advanced Technology Attachment) and IDE (Integrated Drive Electronics) connectors.
The first part of the operating system to load is the kernel.
The kernel acts as a “liaison” between the computer’s hardware and software.

18. How the times have changed
Cohen’s first computer: Macintosh LC II (circa 1993).

20. Apple printers
ImageWriter II: $595 cost ($1,012 in today’s dollars); 144 DPI.

21. Apple printers
StyleWriter II: 360 DPI; also 2 pages per minute.

22. Apple printers LaserWriter: 300 DPI; 8 pages per minute.
Cost: $6,995 (equivalent to $15,576 today).