Client, server, and what the cloud means

02Roles follow the exchange

A picture service can answer your viewer, then request data from another service. It is the server in the first exchange and the client in the second. Name the particular exchange before assigning a role. A computer's size or location does not determine whether its software is acting as a client.

Later lessons explain protocols: agreed rules for communication. For now, follow a request and its response. Being a server does not establish that a service is trustworthy or that you have permission to test it.

Client and server roles in one exchange
A --request for data--> B
A <--response with data-- B

A is the client: it sends this request.
B is the server: it handles the request and sends the response.
If B asks C for data, B is the client in that second exchange.
The same computer can run software in both roles.

A remote original and a saved local copy are on different machines,
even when the copies contain the same data.
The arrows show direction; they do not establish permission or encryption.

03What cloud adds

A cloud service provides computing resources as a service, often on computers operated elsewhere by a provider. The formal definition includes on-demand access and shared resources that can be allocated as needed; a remote computer alone is not enough to establish that it is a cloud service. Cloud data still resides on computers and storage with owners and access rules.

Viewing remote data, saving a local copy and synchronizing copies are different actions. Synchronization means that software sends updates between copies. If no such feature is stated, an edit to a local copy gives you no reason to conclude that the remote original changed. A cloud label alone also tells you nothing definite about privacy or backups.

04Try the conversation cards

This activity changes from the example's note to a picture and includes an explicit Save action. Work with the printed evidence; no live service is needed.

Request, response and local save
Fictional cards; no address to visit or server to start.

Activity cards, out of order:
C: The laptop viewer receives picture data in working memory.
A: The picture service stores the original on its remote disk.
D: The learner selects Save; the viewer writes a local laptop copy.
B: The laptop viewer asks the picture service for the picture.
Assume A happens before this request, and no synchronization is set up.

Put the four cards in order. Label the requester and responder.
After D, draw the two places that hold a saved picture.
Predict whether editing only the laptop copy changes the original.

Separate question exchange:
A browser requests a new note. A note server responds.
Which participant is the client in this exchange?
Answer format: browser or server.

1. Put the Activity cards in order before comparing with the expected A, B, C, D. The remote original exists first; the viewer requests it, receives the data and then saves a local copy.
2. Draw a request arrow and a response arrow. Label the requesting viewer as the client and the responding picture service as the server for this exchange.
3. After the Save action, draw two storage locations: the service's remote original and the laptop's local copy. Explain why receiving data in working memory is different from this explicit file write. Browsers may cache data, but that is not the user-saved document described here.
4. Predict what editing only the local saved copy does. With no synchronization stated, the edit changes that copy; there is no evidence of an update to the remote original. Record what extra feature or event would be needed to support that claim.
5. Keep your diagram for the next boundary lesson. No file was uploaded, no server was started and there is nothing to shut down.

05Optional challenge

Add another exchange in which the picture service asks a thumbnail service for a smaller version. A thumbnail is a small preview image. Label the picture service's role in each exchange. Then explain what evidence would show that either machine saved the thumbnail rather than only passing it through working memory.

06Fresh cases for the checks

Use these fictional cases for the checks below. They have different inputs from the worked examples. Read them here or make notes; no installation or external service is needed.

Birch, Cedar and Spruce are programs on different fictional computers.
Exchange R: Birch asks Cedar for a document. Cedar sends the response to Birch.
Exchange S: Cedar asks Spruce for a preview. Spruce sends the response to Cedar.
No action by Birch is described in exchange S.
The program names do not assign permanent client or server roles.

L: The learner edits the newly saved local copy and saves the edit.
M: Elm responds to Wren with the requested timetable data.
N: Wren asks Elm for the timetable data.
P: Wren writes the data received in this response to a new local document.
No local document exists before this session. The edit is made to the document created in this session.

Remote original on the service computer: meeting.txt contains Room 5.
Saved local copy on a laptop: meeting.txt also contains Room 5.
The learner edits only the laptop copy to Room 8 and saves that local edit.
No upload, synchronization or other change to the service computer occurs.

A program on a laptop asks a remote service for a drawing.
The service responds with drawing data and the laptop program displays it.
No user Save, upload or synchronization is stated.
The service is described only as remote. No access policy, backup arrangement or cloud characteristics are supplied.

07Explain the exchange and the copies

Optional self-check: write a short explanation for someone who assigns each program a permanent client or server label and assumes that viewing remote data saves and synchronizes a local document.

Review your explanation: name a particular exchange before assigning roles, distinguish receiving data from writing a chosen local file, and identify the update event or synchronization feature needed to connect edits across copies. Explain what further evidence you would need for a privacy or backup claim. This explanation is self-reviewed.